The present invention relates to a flexible wire cable or shaft for transmitting torque, compression (pushing) and tension (pulling) forces, or all three-types of forces.
Some prior art push/pull wire wound cables, and some prior art torque transmission wire wound flexible shafts are disclosed in U.S. Pat. Nos. 571,869; 1,811,697; 1,905,197; 1,952,301; 2,000,997; 2,401,100; 3,043,120; 3,192,795; 3,242,691; 3,274,846; 3,705,489; 3,791,898; 3,979,896; 4,112,708; 4,629,707; 4,655,610; and 5,288,270.
Prior art push/pull wire cables which are designed to transmit compression and tension forces usually consist of a central core wire and one or two layers of a group of equal diameter wires helically wound about the core in the same direction with a high pitch angle, typically in the 70° range. Such cables are not suitable for use in transmitting torque because:                a. Since the wire layers are wound in the same direction, they tend to unwind if an attempt is made to transmit torque in a direction opposite to the wind direction.        b. Since the pitch angle is high, most of an applied longitudinal compression Qr tension force is transmitted efficiently through the wires but only a relatively small part of an applied torsional force is transmitted efficiently through the wires. As a result, a relatively large diameter cable of the push/pull construction type is required to transmit a given torsional force, as compared with a flexible wire wound shaft designed to transmit torsional force.        c. Push/pull wire cables of the aforementioned construction are relatively stiff in bending as compared with flexible shafts designed for transmitting torque, such stiffness being an undesirable characteristic.        
On the other hand, flexible wire shafts designed to transmit torque generally consist of a central core upon which multiple layers of wire groups are wound, with adjacent layers being wound in opposite pitch directions, with a substantially lower pitch angle (typically 55° or less, a range of 30° to 55° being preferred) than that of the layers of a push/pull wire cable. This construction results in significantly greater flexibility and higher torque transmission capability for a given diameter, as compared with push/pull cables. However, these shafts have a considerably greater tendency than push/pull wire cables to unwind when subjected to compression forces.
Accordingly, an object of the present invention is to provide a flexible wire cable which exhibits favorable characteristics of both push/pull cables and torsion-transmitting flexible shafts.